There is available on the market today glass substrates, such as large glass windows, which have a pyrolytically applied doped tin oxide film thereon. The purpose of the pyrolytically applied doped tin oxide film is to improve the emmissivity value of the glass substrate over that emmissivity value which it has without the coating thereon. Normally the emmissivity value of the glass sheet is reduced by the application of the doped tin oxide film. A normal glass sheet having a thickness of one-eighth of an inch has an emmissivity value of 0.84, whereas such a glass sheet coated with a pyrolytically applied doped tin oxide film would have an emmissivity value in a range of about 0.50 to 0.35.
The lower the emmissivity value, the better the coated glass sheet is in reflecting infrared radiation. For example, if such a coated glass sheet is glazed into a window with the coating facing the interior of the building, the coating is effective in reflecting back into the building the infrared radiation produced within the building as, for example, by means of a fuel burning furnace. Most of such radiation would normally pass through an uncoated window but will have a large proportion thereof reflected back into the building by a properly coated glass window. Our invention teaches a way of obtaining an even greater reduction of the emmissivity value of a pyrolytically applied doped tin oxide film on the surface of a glass substrate such as a glass window glazing. The method of our invention achieves substantial improvements in the emmissivity value, that is, a lowering of the emmissivity value over structures which are generated not using the method of our invention.